What is e-ink on e-readers like kindle? How does the technology compare to a regular screen?
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It’s basically like an electrically programmable etch a sketch screen.
So it manipulates the pixels magnetically, but it doesn’t need to sustain any power to leave the pixel black. Which is why eReaders have such crazy battery life and can leave cover screens on indefinitely.
It’s electrically controlled pigment. Imagine a page that you could control whether or not there’s ink on a spot by running electricity.
In an LCD screen, there’s an always-on backlight, and then that comes through Red, Green, and Blue filters based on if they’re open or not by an electrical signal. To have any visual, you have to have light coming out.
With e-ink, the only light that you see is reflected from the environment. You don’t have a giant flashlight of a screen in an otherwise dark room.
I read once a long time ago that the paper white Kindles used something like a ping pong ball on the screen. Half of it was black, and the other side was white. The black side has one charge, and the white the opposite charge. You line all these balls up nice and tight with each other.
Kindle sends a charge down the page of these ping pong type balls and some flip from white to black and form black letters on an otherwise white sheet.
When you “turn the page” you send another charge down the page and rearrange the “letters” on the page.
An LED type of screen has individual pixels that light up or don’t light up in order to form letters and pictures.
A pixel on an ordinary screen is a collection of red, green, and blue lights that can shine in different combinations to produce different colours.
The pixels in e-ink displays are tiny capsules that contain positively charged black pigment and negatively charged white pigment. Different colours (white, grey, black) are made by using tiny electromagnets to push different amounts of black and white pigment to the surface of each capsule.
This means that instead of shining light directly into your eyeballs, e-ink displays use natural light and so they’re much less harsh on the eyes. Also it means that the displays can keep whatever image is on them without requiring power. On the other hand, they’re much slower than regular screens because you have to wait for the pigment to settle before you get a clear image.
E-ink works kind of like a magnadoodle, the pigment gets pushed or pulled through some goop depending on electric charge. The light reflecting off of this is what creates the image. Here’s a good video that goes much more in depth than I can: https://www.youtube.com/watch?v=MsbiO8EAsGw
Other modern screens are usually either LCD, which work by changing the polarization of light passing through the display, or OLED where there are tiny diodes that directly emit light.
So it is made of little capsules containing positively and negatively charged ink of two different colours, usually white and black, sandwiched between transparent conductors. Unlike with an LCD, the ink stays where it is put, so a picture driven to it stays driven. The pixel can occupy states between white and black, and because the amount of ink in a capsule is well controlled and static, these are predictable, letting you drive greyscale images.
The backplane is a lot like an LCD – each pixel is a capacitor that’s charged to a positive or a negative voltage by one or more transistors.
To drive the e-ink you connect the counter-electrode on the top side, then drive a rapid series of black and white pixelated images that *add up* to the image you want to end up with, when *added to* the image you started with. Then you disconnect the counter-electrode and the image stays.
The way these images are calculated, the ‘waveform’, is complicated and proprietary. My first job in industrial science was doing another more senior scientist’s job while he invented a new way to do this. It’s surprisingly hard, and makes a huge difference!
Why don’t you just drive the one image you want the first time? Because the grey level is determined by the product of applied voltage and time applied, and it’s *hugely* easier to drive either black or white to your pixel than to drive, like, 50% of the black voltage.
Imagine you have pool of black liquid filled with ping-pong balls. You can controll the balls so they either float or sink. If they float, you see white. If they sink, you see black liquid.
Since there are no light sources, it doesn’t tire your eyes like regular screen, it also does not need electricity to maintain it’s current state. It consumes energy only when changing that state. That’s why shops tell you that battery last for X pages, not for X hours.
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